Blame the Torque Converter, Part 2 - Transmission Digest

Blame the Torque Converter, Part 2

Last month, in Part I of “Blame the Torque Converter,” a 2001 Volkswagen Jetta and a 2002 Toyota Tundra were both thought to have faulty torque converters. Both vehicles had TCC-related trouble codes (the Jetta had a 740 code and the Tundra had a 770 code).
Blame the Torque Converter, Part 2

Torque Converter Tech Tips

Author: Ed Lee

Torque Converter Tech Tips

  • Author: Ed Lee

Last month, in Part I of “Blame the Torque Converter,” a 2001 Volkswagen Jetta and a 2002 Toyota Tundra were both thought to have faulty torque converters. Both vehicles had TCC-related trouble codes (the Jetta had a 740 code and the Tundra had a 770 code).

The TCC codes for both vehicles were found to have been caused by the installation of incompatible hard parts. The overdrive planetary gear set in the Jetta was replaced with an overdrive planet with an incorrect ratio. An overdrive planet was also the part that caused the TCC code in the Tundra, but for a different reason. In the Tundra the input shaft is an integral part of the overdrive planet and is available in two different lengths. The overdrive planet was the correct ratio, but the input shaft was too short to properly seal the TCC circuit in the torque converter.

The following are two more examples of falsely accused torque converters.

2001 Chevrolet Impala 1811 and 741 codes

A 2001 Chevy Impala equipped with a 3.4-liter V-6 engine and a 4T65-E transmission was towed to a transmission shop. The initial visual inspection revealed that the vehicle had the common differential failure, but since there were more than 100,000 miles on the odometer the customer was sold a complete rebuild.

This turned out to be an excellent call on the shop’s part, because the failure was more widespread than could be seen from the outside. When the unit was disassembled, the technician found that the splines on the fourth hub were almost totally stripped off and the plastic thrust washer that separates the drive sprocket from the drive-sprocket support had disintegrated, allowing metal-to-metal contact.

The rebuilding of the transmission and torque converter seemed to proceed routinely, and after a successful road test the vehicle was returned to the customer. About two weeks later the customer returned the vehicle with a P0741 code. The technician who had originally performed the work on the vehicle was on vacation, so the vehicle was checked by the shop owner. The shop owner remembered having a similar problem with another vehicle that turned out to be a defective TCC solenoid, so he replaced the solenoid as a safeguard. He kept the vehicle for a couple of days but was not able to duplicate the problem.

Two weeks later the vehicle again returned to the shop with the same 741 code. The technician initially thought that the differential might have been replaced with one having an incorrect ratio. He remembered that the original differential had a sun gear with 42 teeth, and when he checked the replacement he found that it also had 42 teeth.

He then turned his attention to a possible leak in the TCC circuit. A wet air test showed that the AFL and TCC control valves did show signs of leaks. The AFL, TCC control and TCC regulator valves were replaced. The torque converter also was replaced with another rebuilt unit.

At 65% duty cycle, the slip rate went from 650-700 rpm to 400-500 rpm. Although the TCC slip rate did improve after replacement of the valves and converter, it was still high enough to cause the 741 code.

The transmission was removed from the vehicle again and placed on the bench. The technician remembered robbing the drive-sprocket support from a 4T60-E transmission. He checked with his hard-part supplier to make sure that the 4T60-E and 4T65-E sprocket supports had the same part number. When he found out that the part numbers were different he was sure that he had solved the problem.

Mike Souza from ATSG wrote a great article (Transmission Digest, April 2008) explaining this problem. The technician used the article as a reference to prove that this was causing the P0741 code, but when he applied air pressure to the TCC apply port on the 4T65-E turbine shaft (Figure 1), he got a full stream of air out of the TCC apply port on the 4T60-E drive-sprocket support. At that point he was no longer sure that he had found the problem.

The answer

There is enough clearance between the 4T60-E drive-sprocket support and the 4T65-E turbine shaft to allow enough flow to pass an air check. The customer did not drive in any hilly areas and did not carry any passengers, so the lockup-apply-pressure demand was low. In this situation there was sufficient oil flow most of the time, and the vehicle would set a code only every week or two.

The following figures illustrate the flow-area difference created by the two different supports. Figure 2 shows a small amount of plumbers putty placed on the 4T65-E turbine shaft before it was inserted into a 4T60-E drive-sprocket support.

The putty is being used like Plastigauge® to visually demonstrate the different clearances. Figure 3 shows the putty compressed or removed by the support.

Notice how much more putty remains after the same shaft with new putty was inserted into the 4T65-E support (Figure 4).

2001 Volvo 740 Code

A 2001 Volvo equipped with a 1.9-liter engine and 55-50SN transmission was brought to a transmission shop. The customer complaint was fluid leaking from the front of the transmission. The vehicle had high mileage but performed very well. This was a typical soft-part overhaul and torque-converter rebuild. The only hard part that was replaced was the pump.

On the road test there was no lockup and a P0740 code was set. Of course, the converter came under suspicion immediately, but it was hard to ignore the fact that replacing the pump was the only change made to the unit. The replacement pump was found to be the reason for the 740 code. There are two different-diameter input shafts, 0.844 inch and 0.870 inch, and two different pumps with stator bushings to mate to the shafts. Figure 5 shows a piece of gasket material fitted into the overly large clearance that results when a small shaft is used in the large pump bushing.

Seasoned transmission technicians will remember similar problems with worn bushings or incorrect turbine-shaft rings on the 125C transmissions. The part of the TCC apply circuit that caused problems in the early 1980s is still important today.

Transmission Digest had a Tech Tip about this problem written by Hardparts for Transmissions in the June 2006 issue, and ATSG covered it in its red seminar book in 2007. Today most hard-part suppliers ask for specific applications for this part, or at least the dimensions of the shaft or stator bushings.

The four vehicles in “Blame the Converter” all had TCC-related trouble codes: 770, 741 or 740. With the exception of the Volvo, each vehicle’s converter had been replaced at least one time, and in every instance the converter was blamed but found to be not guilty.

Special thanks to Paul Tinges from Hardparts For Transmissions and ATSG for their technical assistance with this article.

Ed Lee is a Sonnax Technical Specialist who writes on issues of interest to torque converter rebuilders. Sonnax supports the Torque Converter Rebuilders Association. Learn more about the group at

You May Also Like

Trying to Stop the Wheel Hop on Ford Edge with 6F50 Transmission

The 2014 Ford Edge SEL with a 3.5L engine (figure 1) and a 6F50 transmission can also be equipped with an AWD system. This would include a Power Transfer Unit (PTU) attached to the transmission with a rear driveshaft going to the Read Differential Unit (RDU). The RDU comprises a differential assembly along with a

The 2014 Ford Edge SEL with a 3.5L engine (figure 1) and a 6F50 transmission can also be equipped with an AWD system. This would include a Power Transfer Unit (PTU) attached to the transmission with a rear driveshaft going to the Read Differential Unit (RDU). The RDU comprises a differential assembly along with a viscous coupling assembly controlled by an Active Torque Control (ATC) coupling solenoid. The system is designed to monitor vehicle conditions continuously and seamlessly adjust torque distribution between the front and rear wheels. When it is functioning correctly, there should be no perception of this taking place when launching or driving the vehicle. 

Sherlock Holmes Approach to an AB60 No-Move Situation

The effectiveness in diagnosing automatic transmission malfunctions is an art form. Although there are similarities among the wide varieties of transmissions on the road, each transmission has its own peculiarities. Aside from having mechanical, hydraulic, and electrical hardware systems to contend with, software/programming issues and various vehicle platforms make diagnostics much more difficult.  Related Articles –

GM 6T40 Pump Identification Guide

The 6T40 was introduced in 2008 for General Motors front-wheel-drive cars in the Chevrolet Malibu and has gone through several changes throughout its three generations, specifically in the pump area. The 6T40 is closely related to the more lightweight 6T30 and the heavier duty 6T45 and 6T50. Generation one started phasing out during the 2012

Seeing the Forest AND the Trees

They say that the proverbial phrase “I couldn’t see the forest for the trees” means that a person or organization cannot see the big picture because it focuses too much on the details. Related Articles – TASC Force Tips: Hydraulics Fundamentals: Check Valves – Shift Pointers: Mazda Sensitive to Pressure – Transmission Testing & Repairs:

The Manifold Pipeway

The Honda six-speed transmission has been on the bench of many specialty shops for one reason or another (figure 1). But, for those of you who have yet to lay your hands on one, mounted on the upper side of the unit is one of the largest, if not the largest solenoid and pressure switch

Other Posts
6R80 whirring noise: TCC slip or engine surge?

About a month ago, we at Certified Transmission received a 2015 Ford Expedition 4WD at the shop. It was equipped with a 3.5L Turbo V6 engine and a 6R80 transmission. The complaint read, “RPMs fluctuate up and down and there is a whirring noise.” The vehicle was brought to us by one of our wholesale

Alto releases friction and steel module for ZF 6HP transmissions

Alto has introduced a new friction and steel module for ZF 6HP series transmissions. The module works with ZF 6HP19/X/A (model years 2004 and on) and ZF 6HP21/X (model years 2007 and on) for ZF, Audi, BMW and Volkswagen vehicles. Related Articles – Toledo Trans-Kit adds transmission kits for Aisin A466, RE6R01A – Toledo Trans-Kit

Sonnax unveils valve kits for ten-speed Ford, GM transmissions

Sonnax highlights its valve kits for Ford and GM ten-speed transmissions. Related Articles – Milton Industries introduces new AirStrike air hammer – K-Tool offers Ultimate Torq socket sets  – Alto introduces Nissan high-performance friction, steel module The first of these is a line of oversized main pressure regulator valve kits #105740-20K (pictured above) for GM

Volkswagen dual clutch transmission and direct shift gearbox: What you need to know

Most of the drivers who own a Volkswagen car or truck with a Direct Shift Gearbox (DSG) will not know they have a dual-clutch transmission connected to the engine. Most of them will think they have an automatic that gets excellent gas mileage. It is not until a transmission component fails or a service interval